FAIRFAX, Va. — The Republican establishment has a message for John Kasich: get out, and get out of Marco Rubio's way.

A string of elected officials, GOP insiders and prominent donors officially threw their support behind Rubio on Monday, calling him their last chance to take down Donald Trump. Their statements had another common theme. Some explicitly called for Kasich to quit, while others sent the same message by saying the Ohio governor's ongoing presence is holding Rubio back.

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“If at some point John were to decide not to go forward with his campaign, Marco would be the primary beneficiary of that decision,” former Minnesota Gov. Tim Pawlenty told POLITICO after his official Rubio endorsement. “It’s not for me or anyone else to say when John should stay in or get out but … John’s decision to stay in or get out could have a marked impact on the race.”

This is not what Kasich had in mind: He had hoped that if he could be the last governor standing, his record and experience would persuade party power brokers to unite behind him in a challenge to Trump and Ted Cruz. Pushing that point, Kasich's campaign issued a statement after Jeb Bush dropped out declaring Kasich winner of the "governor's bracket."

Utah Sen. Orrin Hatch on Monday threw his support behind Rubio, and he said it would be helpful to Rubio for Kasich to drop his bid. "It would be, but that's up to John and John's got every right to stay in the race," Hatch said. "But sooner or later, it's got to come down to Marco if people really look at it carefully."

Rubio’s second-place finish in South Carolina — and Bush’s decision to drop out — cemented the Florida senator’s edge in the race for establishment favorite. And the Kasich camp's hopes for the party to take a “wait-and-see” approach until the Ohio primary took a hit over the weekend, with Trump following his New Hampshire landslide with a South Carolina rout and driving establishment anxiety that “The Donald” is unstoppable.

“At the end of the day, you have to try to stop Trump, and then you might have to live with Trump,” said a longtime Republican fundraiser aligned with Rubio. “I’m realistic. I think Marco is the best chance to stop Donald Trump, and I certainly think he’s the best candidate of the candidates we have to beat [Hillary] Clinton.”

The fundraiser added that Kasich, while well-respected among the donor class, just doesn't have the organization to mount a serious challenge. "This thing is now warp speed," he said. "If you don’t have infrastructure, you’re gone."

Rubio himself is working tirelessly to box out Kasich. In a celebratory address following a second-place finish in South Carolina, he declared it a "three-man" race, a reference to himself, Cruz and Trump — but not Kasich.

It's not all dark news for Kasich. Former Govs. Tom Ridge of Pennsylvania and Bill Weld of Massachusetts threw their support to Kasich Monday afternoon. Kasich has nabbed Ken Langone, the Home Depot co-founder who backed New Jersey Gov. Chris Christie through New Hampshire, and The New York Times reported Monday morning that billionaire financier Stanley Druckenmiller lined up with Kasich too.

Kasich’s challenge now is to convince Republicans he has a credible chance to become the party’s nominee, and that challenge is coming during a particularly difficult stretch of the election for him. Kasich's strength is in Northern states, but the next big test is March 1, this year's version of Super Tuesday when a dozen, mostly Southern states hold their nominating contests simultaneously.

He’s pinning his hopes on picking off moderate states like Massachusetts and Vermont — which vote on March 1 — but polls don’t bear out his strength there. An Emerson College poll released Monday morning showed Trump with an enormous advantage, with Rubio a distant second and Kasich close behind him in third.

Kasich's best hope may be Ohio, which will dole out 66 delegates in a winner-take-all primary on March 15. But he has to make it there first, and Republicans continue to line up behind Rubio in the meantime. Nevada Reps. Cresent Hardy and Mark Amodei announced their support Monday, as did Nevada Sen. Dean Heller. Arkansas Gov. Asa Hutchinson, Sens. Jeff Flake of Arizona and Thom Tillis of North Carolina also backed Rubio on Monday as well.

The Rubio campaign has recently won support from Ambassadors John Rood and Francis Rooney, as well as prominent Kentucky-based donors Kelly Knight and Joe Craft, Chicago investor Muneer Satter and Bobbie Kilberg, a prominent Republican fundraiser, who supported Christie and Bush before their exits from the race.

“I think it is not helpful to have more than one mainstream candidate in this race,” said Kilberg, in a phone interview. Kilberg praised Kasich, but she said she now sees Rubio as the only establishment-backed candidate with a credible path to the nomination.

Kasich's campaign has always run on a relatively shoestring budget, and he'll struggle to amass the resources needed to scale his operation into a true national organization. Asked whether the campaign is running ads in any of the dozen states voting on Super Tuesday, a spokesman pointed to reports about his super PAC going on the air.

“They’re essentially trying to run a residual New Hampshire campaign in Massachusetts,” the Rubio-aligned donor said. “They’re trying to go back to the well and it’s dry. John Kasich has every right to be in the race but he doesn’t have the right to be in the race if he’s not running a serious campaign — and a serious campaign would constitute ads in Vermont, ads in Massachusetts to get a win. Otherwise, he’s just prolonging.”

None of this means, however, that Kasich has any intention of heeding those calls, and on Monday he said he's not going anywhere. His team has projected confidence, describing a campaign raking in donations since New Hampshire.

"They thought we would have a nominee by some point in March. This is going to be a race that’s going to go much deeper into the calendar," Kasich's top strategist John Weaver told reporters Saturday, ahead of South Carolina's vote. "The Kasich brand of being uplifting and inclusive, of having a conservative reform agenda that can be enacted and can be positive is a growing force in national politics. ... We do believe that it will be a one-on-one race with Donald Trump."

After drawing a crowd of about 1,000 to George Mason University here, Kasich defiantly told reporters that he has no plans to fold — and he added a new twist: He’s an anti-establishment candidate now.

“I’m not gonna go shut something down because a bunch of people in the inner city of Washington who frankly never liked me from the beginning are going to tell me what I’m gonna do,” he said.

“I think it’s funny. I think it’s ridiculous,” he said with an audible guffaw, when asked about Rubio world’s effort to nudge him out of the race. “I don’t take orders from K Street, from inner rooms, from lobbyists, I’ve challenged the establishment my whole career.”

Asked whether he’d consider appearing on a presidential ticket behind Rubio, Kasich retorted: “Sure, if he wants to run for vice president with me, that’d be great. Are you kidding? I don’t run for second.”